Armatures for induced current torque transmitting apparatus



Dec. 11, 1956 H. s. JACOBS ErAL 2,773,998

ARMATURES FOR INDUCED CURRENT TORQUE TRANSMITTING APPARATUS 2Sheets-Sheet 1 Filed March 1 1954 INVENTORS W%GMZL Mal/M AT TORNEY Dec.11, 1956 H. s. JACOBS ETAL ARMATUREIS FOR INDUCED CURRENT TORQUETRANSMITTING APPARATUS 2 Sheets-Sheet 2 Filed March 3 1954 5 m m T m 7 NO 3 E T W T o l A E E P s P 4 5 3 United States Patent ARMATURES FORINDUCED CURRENT TORQUE TRANSMITTING APPARATUS Henry S. Jacobs,Shorewood, and Jeremiah M. Curtin,

Milwaukee, Wis., assignors to Hamischfeger Corporation, Milwaukee, Wis.,a corporation of Wisconsin Application March 1, 1954, Serial No. 413,096

7 Claims. (Cl. 310-105 This invention relates to induced current torquetransmitting apparatus and more specifically resides in an armature forsuch apparatus having a flux conducting drum of magnetic material thatsupports circumferentially spaced inductor bars of low resistance andreactance with cooling fins of resistance greater than that of the barsattached between the ends of the bars to form current paths extendingbetween the bar ends that limit the inductor bar currents and impart tothe torque transmitting apparatus enhanced speed-torque characteristicsin which output torque is of a substantial value over a wide range ofoperating speed.

The torque of a Wound armature induced current torque transmitter,having an external resistance forming a part of the armature circuit,may be varied at will for any given slip-speed by a simple variation ofthe value of the external resistance. Also, through a variation of theresistance with changing slip-speed high torque output over asubstantial speed range may be attained. Self-contained armaturecircuits, on the other hand, do not permit such flexibility of operationthrough control of an external secondary resistance. The self-containedcircuit is usually of the so-called squirrel cage type in which thearmature inductor bars are short circuited one to another at their endsby end ring connections. In some instances cooling fins are disposedbetween the ends of the inductor bars and the short circuiting endrings. Such cooling fins act as inductor bar extensions that aredisposed outside the working flux field for enhancing the rate ofdissipation of heat that is evolved in the armature circuit. Whether ornot such fins are employed, the circuit characteristics are fixed in theself-contained circuit and there is no provision for the variation ofresistance through an external variable control.

For operating in the low slip-speed ranges the higher output torquevalues are obtained by employing a low resistance in the armaturecircuit. Conversely, in the higher slip-speed ranges the higher outputtorques are attained through the insertion of substantially higherresistance values in the armature circuits. It has been a commonpractice to provide an armature, with a selfcontained circuit, that hasthe characteristic of a low resistance circuit at the low slip-speedsand of a high resistance circuit at the higher slip-speeds, by placing adouble cage in the armature. Such double cage has two sets of inductorbars, one of which is deeply embedded in the magnetic drum to produce ahigh reactance at high slip-speeds that effectively precludes currentflow in this set of bars at such speeds. In this manner dual resistancecharacteristics are provided to enhance the torque output over anextended speed range.

The use of a double cage introduces a high reactance in the armaturecircuit which sharply curtails the maximum attainable torque output.Further, the resistance in the rotor bars extending through the magneticdrum causes the bars to become principal sources of heat evolution. Thisis particularly pronounced at the higher slip-speeds. Such heat must beeffectively dissipated in Tue order to enjoy a sustained high level oftorque output. While the problem of heat dissipation may not be vital inmotor applications, it becomes of paramount importance in the operationof induced current clutches and brakes.

Rapid heat dissipation is necessary to retain thermally induceddimensional changes at a minimum and to avoid disruptive internal forcesthat may occur upon undue temperature increase in the magnetic drum. Itis particularly desirable to have the evolution of heat occur outsidethe magnetic drum and to this end, in the practice of this invention,the inductor bars are of large cross section with a substantialcircumferential width and a relatively shallow depth. The inductor barsthen present a minimum of resistance and reactance to the armaturecircuit. Cooling fins with large surface areas and of resistancesubstantially greater than that of the bars are then joined to the barends to act as bar extensions through which the induced currents flow.The resistance of the fins causes the major evolution of heat to occurprimarily within the fins and outside the magnetic drum. The cooling airthat is passed across the fin surfaces carries away and rapidlydissipates the evolved heat.

The use of low resistance, low reactance rotor bars for the entireintended range of operating slip-speeds dispenses with the use of adouble cage rotor bar construction which has heretofore limited peaktorque output. A desirable variation in resistance with change inslipspeeds is provided in this invention by providing the major currentlimiting resistance in the armature circuit in the cooling fins. Thevalue of the resistance may be selected to develop a desiredspeed-torque characteristic and the fins may be comprised wholly, or inpart, of magnetic material that effects a change in resistance withslip-speed. The resulting variation in resistance provides for uniformlyhigh torque output over a substantially wide operating range ofslip-speed.

It is an object of this invention to provide an armature for an inducedcurrent torque transmitter having cooling fins that impart a resistanceto the armature circuit that varies in value with slip-speed to provideenhanced speed torque characteristics for the apparatus.

It is another object of this invention to provide an armature for aninduced current torque transmitter in which the armature circuitresistance and reactance characteristics are dominated by that ofcooling fins forming inductor bar extensions.

It is another object of this invention to provide an armature for aninduced current torque transmitter with cooling fins connected to theends of the inductor bars that are securely fastened in position towithstand severe rotational forces encountered upon abrupt accelerationsand decelerations.

It is another object of this invention to provide an armature for aninduced current torque transmitter of low inertia for obtaining rapidacceleration and deceleration.

It is another object of this invention to provide an armature for aninduced current torque transmitter in which heat evolution that occursin the secondary circuit is localized in current conducting cooling finsto the side of the magnetic drum carrying the inductor bars, which finsare advantageously disposed for rapid dissipation of the heat evolved.

It is another object of this invention to provide an induced currenttorque transmitter in which inductor bars. of relatively large crosssection disposed near the surface of a magnetic flux conducting drum areemployed to present a minimum of resistance and reactance. to thesecondary circuit.

7 These and other objects and advantages of this in vention will appearin the description to follow. In the systems 3 description-reference ismade to the accompanying "drawings which form a part hereof and in whichthere is shown, by way of illustration and not of limitation,

"specificforms in which this invention may'beernbodied.

In"'the drawings:

"Fig. 1 is an end view in section with parts broken away of an inducedcurrent torque transmitter in the form of a clutch and in which thisinvention is embodied viewed through the plane 1l shown in Fig. 2,

'Fig. 2 is a side view in section of the clutch viewed through the plane2-2 shown in Fig. 1,

Fig. 3 is a fragmentary end view in elevation of the induced currentmember of the clutch,

"Fig; 4 is a fragmentary view insection of an alterna- "tive form of aninductor'bar end and a cooling fin attachedthereto viewed through'theplane 4 S shown "in'Fig. 2,

Fig. S-is' a fragmentary side view with parts broken away'and in sectionof the inductor bar end and cooling fin shown in Fig. 4, and

"Fig. 6 is a graph of speed-torque characteristic curves that-maybeobtained in the use of the clutch.

"Referring'now to the drawings, there is shown in Figs. '1 and 2 aninduced current torque transmitter in the 'form'of'a clutch '1. Theclutch 1 has'an input shaft 2 to which is keyed'a hub 3 that supports acircular shroud plate'4. On the inner face of the shroud plate 4 there"is'secured a cooling air deflecting battle 5 in the form 'of'a'circularband, and extending radially between the hub 3 and the inner face of thebaffie 5 is a plurality of circumferentially spaced bracing webs 6 thatreinforce material which supports on its inner circumferential face 'aplurality of uniformly spaced pole 'pieces 10. The

pole pieces 10 are individually secured to the'magnetic *frame 9 bymeans of boltsll and surrounding each 'pole'piecelfl is'a'field winding12. Upon an energization o-f'the windings 12 through usual connectionsnot shown, alternatenorth and south magnetic poles Wlll be formed at theinner 'polefaces of the pole'pieces 10,

from 'whichmagnetic flux will extend for interception by an armature tobe described.

"An' output shaft 13 in the form of a quill surrounds the inputshaft 2,as is shown in Fig.2, and a pair of tapered bearing sets 14 insertedbetween the shafts 2 andlS-provide for both the support of and theindependent rotation of the shaft 13. Carried by the" shaft 13 is anarmature, or induced current member, generally designated by the numeral15 that intercepts and conducts the-magnetic'fiuxextending from thepolepieces 10. The

armature 15 has a hub 16 keyed to the'output'shaft 13 andboltedtoone'side face of the'hub-16is a bearing "retainerl'lfor axially-aligningthe-bearing sets 14=w1th the armature assembly. -A pair of transversediaphragm plates 18 encircle and are firmly secured to-"thecutercircumferential face of thearmature hub 16. Supported by the diaphragmplates 18 is a plurality of spoke plates 19' that extend axially andradially outwardly. The plates 19 are paired, with the plates of eachpair being convergent outwardly to support a bolster 20 that has an*arcuate circumferentiallyextending outer 'face in supporting relationwith a magnetic' drum'21. Thedrum "21 is formed of a' plurality oftransversely extending stacked laminations 22 and is rigidly secured tothe'bolsters 20, and hence the spoke plates'19, so that the torque reaction of the apparatus may be transmitted to the'output shaft 13 withoutadverse effect. A material-"of low thermal conductivity, such as astainless steel,-isjpreferabIy employed for the spoke plates 19 andbolsters -20 'to inhibit the" conduction "of heat, "which maybe evolved"in'thexdrum 21,to"retain"the hub 16 and-the supporting shaft 13 andbearings 14 relatively cool.

Embedded in slots that extend axially across the outer circumferentialair gap surface of the magnetic drum 21 is a plurality of low resistanceinductor bars 23. As shown in Fig. 3, theradially outer surface of eachconductor bar 23 is flush withthe =air'gap surface of the drum "21..Toretain :the bars 23 in position, a groove is cut in the side faces ofeach bar, with corresponding mating. grooves being'formed in theadjacent slot faces, and a key rod 24 is'inserted in'each set of matinggrooves. The ro'ds24are driven in place for a tightfittosectlrelyholdthebars 23 from loosening and shifting position. Each bar23 is preferably given a substantial circumferential width and arelatively shallow depth so that the reactance will be small. Also, byplacing the bars 23 flush with the air, gap surface of the drum. 21 amaximum of working fiux'will be intercepted and the leakage flux iscorrespondingly reduced. The ends '25 'of'the inductor bars 23 extendaxially beyond and overhang the magnetic drum '21. A sleeve 26 ofweldable'material is'fittedover each inductor bar end 25. The'sleeves 26may be constructed from fiat stock which is turnedto form an enclosedloop with theresulting'searnfbeing welded, as is shown in Fig. 4

at 27,or maybe formed 'in'other' suitable manner. By brazing the sleeves'26 to the inductor bars 23, which normally are of'copper or similar lowresistance conducting material, the sleeves will be firmly secured inposition. The sleeves 26 then provide firm anchorages for the support ofa plurality of cooling fins 28.

The radially extending cooling fins 28 are constructed with outersurfaces of weldable material and each is attachcdby Welding at itsradiallyouter end to the inner face of a'sleeve 26. Each fin 28terminates at its radially inner'end' in a welded connection with a hooplike end ring'29 thatis supported' by a plurality of axiallyextendingbrackets 30 that project from a diaphragm plate 13. like endring assemblies are provided on each side of-the armature 1L3, andeachend ring 29 is formed of an inner-rim '31- of a highly conductivematerial, such as copper, and-an outer rim 32 of -a strength impartingweld- I transmitter are of'la'rge cross section area to present a verylow resistance to'the armature circuit, and this permits the selectionof cooling fins'28 that'will have'a substantially greater resistance,but in which the overall resistance ofthe armature circuit is small 'toprovide .the wanted hi'gh'torque'output at low slip-speeds. By enablingthe'fins 28' and, :if' desired, parts of. theend rings 29, to: comprisethe eifective resistance in the'armaturc circuit evolutionof' heatwill'occur principally within'the fins f2? and the-end rings29, ratherthan in the bars 23 embedded in the magnetic drum 21. I that for optimumoperation, wherein thermalsexpansion It has been found and thermally.induced stresses in'the armature/drum 21 are not. excessive, that theohmic, or-udirect current,:-re-

- sistance -of. the fins 28 compared toithat of the bars -shouldnot beless than the ratio. 10:1.

' For the high slip-speeds it is desirable to have substantialtorqueoutput to :quickly bring the driven member up' to runningi'speed,in theiinstanceof a'clutch, .orto a standstill; in the instance of abrake. I It is necessary,-then, to employa substantially largerresistance in the-armature circuit, asic'ontraste'd' w-ith-thatofloufslipespeed operation, fobcieaitihg-dhe -necessary tUrque. The?high armature circuit resistarice-must be localized'outside madam-'21and the low resistance bars 23. Excessive heat evolution within the drum21 will then be avoided for high slipspeed operation as well as lowslip-speed operation. In the present invention the larger circuitresistance for the higher slip-speeds may be attained by selecting a lowresistance magnetic steel for the cooling fins 28 that will introduce aso-called skin effect into the armature circuit. During low slip-speedoperation the current passing through the fins 28 will be distributednearly uniformly throughout the fin cross sectional area. The fins 28then present a minimum of resistance to current flow and torque willincrease rapidly as slip is slightly increased from the zero value, asis shown by the curve 33 in Fig. 6.

As slip increases the frequency in the armature circuit correspondinglyincreases and the magnetic field of self induction will give rise to theskin effect phenomenon in the fins 28. Being of magnetic material whichprovides a low reluctance flux path for the self induced flux, the fins28 will exhibit a marked crowding of the current passing therethroughtoward the outer surface, or skin. This crowding of current pronouncedlyincreases as the frequency of the induced currents increases. Thecrowding leaves the center cross section areas nearly void of currentand the effective resistance of the fins 28 is thereby substantiallyincreased with increased slipspeed. The increasing resistance withincreasing slip-speed causes a high level of output torque to bemaintained, and as is shown by the curve 33 the output torque may bemade nearly constant over an extended range of working speed by properselection and proportioning of the fin material.

In some applications it is desirable to attain a torque speedcharacteristic presenting a somewhat reduced torque at the largerslip-speeds, which torque is, however, sulficient to cause a rapidchange in speed of the output shaft without severe shock being impartedto the driven apparatus. The curve 34 in Fig. 6 is an example of such atorquespeed characteristic, and in Figs. 4 and 5 there is shown acooling fin 28' that may be employed in attaining the curve 34. The fin28 comprises a thin central lamina 35 of a low resistance material suchas copper that is flanked by outer laminae 36 of strength impartingweldable material, such as a stainless steel. The outer laminae 36 arewelded to the associated sleeve 26 and the outer rim 32 of the end ring29, similarly as the fins 28 of low resistance magnetic steel.

The copper and steel laminae 35, 36 are proportioned to give asufficiently low resistance for a substantial torque output at the lowslip-speeds. The magnetic effects of a stainless steel will not be asmarked as for the highly magnetic fins 28, and as slip-speed nowincreases the resistance will not increase as greatly as for the fins 28producing the curve 33. The resistance, however, may be sufficientlyhigh for attaining a desired level of torque output for the higherslip-speeds. The curve 34 is representative of a speed torquecharacteristic that may thus be attained. Apparatus having acharacteristic curve like 34 finds use in instances where a devicemoving in one direction is to be rapidly reversed, but where reversal isto be accomplished without shock or severe stresses being transmitted tothe driven device as the reversing torque is first applied. An excavatorcab, for example, with a loaded extended dipper may be rotating in onedirection and rapid reversal in the direction of rotation is to beaccomplished without endangering the equipment. For optimum speed ofreversal the initial reversing torque should be less than the peaktorque, and the torque should gradually increase as deceleration of thecab occurs. If the highest slip-speeds of the curve 34 be thoseencountered upon applying reversing torque to the cab, then the lowertorque values at these speeds will commence a deceleration of the cabwithout unwanted shock. As deceleration proceeds torque increases, andas the cab reaches standstill torque will be approaching a maximum. Withthe occurrence of acceleration in the reverse direction torque will bemaintained at high levels.

A combination fin having a central lamina of low resistance copperflanked by reinforcing laminae composed of iron or steel may also beadvantageously employed to reduce the weight of the fin construction,thereby reducing the inertia of the armature. Quicker reversal, orchange in rate of rotation, is then made possible. Likewise, a similarweight reduction in the construction of the end rings will furtherenhance the armature inertia characteristic to provide for rapidaccelerations and decelerations.

By altering the proportion of copper and stainless steel in the fin 28'the torque-speed characteristic may be altered. The curve 37 in Fig. 6,for example, is representative of an armature employing fins with areduced proportion of copper. The resistance at low slip is higher thanfor the fins of curves 33 and 34, and as slip-speed increases theresistance remains high for increased torque output. Other outputcharacteristics may be attained by employing fin materials of increasedmagnetic characteristics with a copper lamina, or by other alterationsin the selection and proportioning of the fin materials which will occurto one proficient in the art without departing from the invention.

There is thus provided a torque transmitter having a low level of heatevolution in the magnetic armature drum, wherein the dominant resistanceof the armature circuit is disposed outside the drum to cause theprincipal heat evolution to occur in cooling fins having a variableresistance with change in slip-speed to provide desirable high leveltorque output.

In the employment of induced current clutches and brakes under extremelysevere load conditions wherein accelerations and decelerations arefrequent and rapid as, for example, may be encountered in the rotationof an excavator cab or in the crowding and retracting of an excavatordipper, the armature must be capable of withstanding large rotationalstresses. To furnish adequate strength a weldable material is employedfor the cooling fins 28 that may be firmly secured to supporting membersthrough the agency of high strength welds. Connections with the copperinductor bars include jacketing the inductor bar ends with the sleeves26, which are likewise composed of a weldable material, and which willnot part from the bar ends 26 under the most severe stresses. Similarly,the end rings 29 present a surface of weldable material for attachmentof the inner ends of the fins 28, thereby providing an apparatus ofenhanced strength capable of withstanding large rotationally inducedstresses. It is to be understood that end rings employed in conjunctionwith the cooling fins are not limited to the form of a laminatedconstruction. If desired end rings may be formed of a homogeneous material and for high strength welds with the cooling fins it ispreferable to have an end ring material like that presented by thecooling fins.

We claim:

1. In an armature for an induced current torque transmitter thecombination of a drum of magnetic material having a circumferential faceforming an air gap surface concentric with an axis of rotation, aplurality of circumferentially spaced inductor bars of low resistivitysupported by said drum having axially extending ends projecting fromsaid drum, a plurality of electrically conductive laminated cooling finsof a resistance substantially greater than that of one of said inductorbars each having a current conducting lamina of copper and a secondcurrent conducting lamina of strength imparting ferrous materialadjacent and supporting said copper lamina, and connections joining saidcooling fins between the ends of said inductor bars with each finforming an extension of an associated bar to provide current paths.forr. the'ftlow ,of 1 inductor bartcurrents whichiare limited invalue'by said cooling fins. Y

.2. .In-ian armatureforlan induced current'torqueitrans .rnitter. thecombination of-a drum of magnetic material having a circumferential'faceforming an air gap surface concentric with an axis of rotation, aplurality of circum'ferentially spaced inductor bars of low resistivitysupported by saiddrum'having axially extending ends projecting from'saiddrum, a plurality of thin'laminated electrically conductiveelongatedfins with relatively large cooling surface areas each formed ofa conductive central lamina of a low resistivity comparable to that ofsaid inductor bars and a flanking lamina on each side of thecentrallamina .of acon'duc'tive magnetic material whereby each fin hasan effective resistance that increases with increase in frequency of acurrentpassing therethrough concentric with anaxis of rotation, aplurality of circumferentially spaced inductor bars of low resistivitysupported by said drum having axially extending ends projecting fromsaid drum, a plurality of tubular sleeves of weldable material eachclosely surrounding and securely fastened to a projecting inductor barend, a plurality of thin electrically conductive cooling fins each ofsubstantially greater resistance than that of one of said inductor "barsand having a face area of weldable material with one edge abutting asleeve on an inductor bar end at a point radially inside the sleeve, theabutting edge of each fin being securelywelded to the associated sleeve'with the fin extending from the abutting edge to an op positelydisposed end'ring connected edge, and end ring connectionsj'oiningthe'end ring connected edges of the 'fins to one'another including'aring of low resistance conducting material "and 'asecond ring ofstrength innparting weldable material attached to said low resistancering with weldsjoining'said second ring and the end ring connected edgesof saidfins.

4. 'In an armature for an induced current torque transmitter thecombination of a drum of magnetic material having acircum'ferential'faceforming an air gap surface "concentric with anaxis'of rotation, a plurality of circumfereritiallyspaced'in'ductor'barsof low resistivityembedded' in said drum having axially extendingendsprojecting from said drum, a-plurality' of tubular sleeves of weldablematerial each 'encircling'aprojecting end of an'inductor tar an securelybrazed thereto, a plurality of electrically conductiveilarninafed'cooling'finsof a resistance substantially greater than that'of oneofzsaidvinductor bars each having a'cur'rent eonductinglamina ofcopperand a sec-- ond current conducting lamina 'of'strength impartingweldable material adjacent and supporting said copper lamina, each "finhaving an edge abutting and securely welded to a' sleeve encircling aninductor bar and extend ing from'the'inductor bar'to an end ringconnectingedge, and end ring connections comprising a ring of lowresistance conducting material and a second ring of strength impartingweldable material reinforcing saidlow resistance ring With welds joiningthe reinforcing ring with the end ringrconnecting edgesrof said fins.

5. In an armature'for an induced current torque trans- 'initter thecombination of a drum of magnetic material having a circumferential faceforming an air gap surface concentric with an axis of'rotation, aplurality ofcircumferentially spaced inductor bars of low'resistivitysupported bysaid drum having axially extending ends projecting from saiddrum, a plurality of tubular sleeves 'of weldable material eachcloselysurrounding and securely fastened toa projectinginductor bar end, aplurality of thin electrically conductive cooling fins each ofsubstantially greater resistance than that of one of said inductor barsand having a face area of weldable material with one edge abutting'asleeve on aninductor bar end, the abutting .edge'of each fin beingsecurely welded to the associated sleeve with the fin extending from theedge to an oppositely disposed end ring connected edge to form a currentpath extending from the associatedbar, and end ring connections joiningthe end ring connected edges of the fins to one another to form currentpaths between bar ends for the flow of inductor'barcurrents which-arelimited by theresistance of said fins.

6. An armature for an induced current torque transmitterin accordancewith claim 1 in which the ohrnic resistanceof-each cooling fin is notless than ten times that of the associated inductor bar.

7. Anarmature for an induced current torquetransmit- 'ter in accordancewith-claim 1 in which an end of each inductor bar is capped with aweldable @material, the strength imparting laminaiof each fin is ofWeldable material, and'the connections joining the cooling fins toinductor bar ends comprise Welds.

References Cited in the file of thispatent UNITED STATES PATENTS 862,776Waters Aug. 6, I907 991,626 Lord May 9, 1911 1,156,364 McColluin Oct.12,1915 1,851,155 Schmid-Burgk Mar. 29, 1932 2,188,398 Bernard Jan. 30,1940

